Got a grown-up crush?

Take a look at the science behind your lust. By Kate Molloy

You're in a happy, committed relationship with a man you truly love. So why do you go all 20-something when Graham from IT walks past your desk? Before you read too much into that ‘chemistry', take a look at the science behind your lust...

Apparently, it doesn't matter how old or sensible you are or how many years ago your Simon Le Bon crush expired - when you're attracted to someone it can do funny things to you. As in, funny body-and-mind-altering stuff that's so powerful you can be seduced into doing the ridiculous and the destructive - all because you believe that this could be something great, something unique and life-altering. But before you stumble into anything, from a mild flirtation to a full-blown affair, consider this: it's probably just a crush. Or you're horny (remember that feeling?). That's not condescending or flippant - it's science. And once you understand what's behind what is, essentially, lust, it's easy not to take it quite so seriously...

Lust at first sight

It takes less than one second to decide if we find someone physically attractive, according to anthropologist Dr Helen Fisher, who has studied the nature of lust and love for more than 20 years. Our brains then scan the rest of him for suitability. So, we'll clock his height (as a rule, we like tall men...) and the way he speaks (...with deep, full voices. We'll make an exception for David Beckham). So, why the preferences? As Allan and Barbara Pease explain in their book, 'Why Men Want Sex and Women Need Love' (Orion, £12.99), it all comes down to biological hard-wiring. Our lust has ensured the survival of the human race.

In fact, Allan and Barbara believe there are three stages of love - sex drive or lust, romantic passion and long-term attachment - and these occupy different areas of the brain, so one does not necessarily have a knock-on effect on another. In other words, you can love one person and really fancy someone else - again, blame the mammal in us. This biological love system (probably more applicable to men), means that you could be in a stable relationship while creating offspring elsewhere.

As women, we're programmed to find the best mate possible, someone who can give us healthy children and care for us. "While men's lust is based almost purely on physical attraction, for women, it's about resources," explains Allan. "You're biologically hard-wired to seek out men who can look after you. In cavemen days, that meant finding someone who could physically protect you and hunt for you. It now means being financially capable of looking after you."

So, despite the fact we're now just as likely to be the breadwinner, we like a tall man not just because it shows that he's healthy and likely to provide us with healthy children, but also because we associate height with wealth.

"In Western cultures, tall men tend to have higher socioeconomic status than short men," explains Cindi Meston, author of 'Why Women Have Sex' (The Bodley Head, £12.99). "In fact, each extra inch can equal thousands more pounds in his salary. It's estimated that 6ft men earn more than £100,000 across a 30-year period than men who are 5' 5". This explains a lot about (6'2") Donald Trump, at least. an attractive upgrade Then why, if you've got your man, would you be attracted to someone else? Well, here comes the uncomfortable bit.

Some anthropologists would argue that your lust-crush is genetically superior to your partner. Men, it seems, were created to spread their seed wherever they could, and women to take that seed and care for it for the rest of their lives. So, genetically, men don't have the predisposition to settle down in the way women do. Therefore, it is the less desirable men who will choose to settle - and now someone better has come along... Um, this is just getting awkward. Let's move on....

Clearly, biology can't explain everything. Firstly, there are social and cultural explanations behind marriage and monogamy, and secondly, we're not just rampant gold-digging cavewomen. Some of us even have a thing for short men - hello, Richard Hammond. In the last 30 years, psychology has played a bigger and bigger part in explaining attraction.You know the feeling. A man walks into your office and you're instantly attracted. There's something about him, something that feels so familiar, yet you've never met before. It must mean something, surely. What else would explain this instant connection? Well, for starters this would: The encounter has just keyed into a past, formative experience.

In other words, there is something about this person, something so subtle that consciously you don't even recognise it, that reminds you of someone else. "This could be a positive thing that you want to recreate," explains relationship psychologist Susan Quilliam. It might simply be that he has a smile that reminds you of someone who cared for you in your childhood, and subconsciously you're transferring the affection you feel for them onto this stranger. (A 2008 study at the University of Pecs in Hungary found that both men and women show preferences for facial structures that resemble their parents'.) "Or it may come from a ‘faulty' situation that you want to resolve," adds Susan. "For example, you may be attracted to someone who resembles your ex because subconsciously you are trying to ‘put right' whatever went wrong in the relationship."

The hormone factor

If in doubt, blame your hormones. A host of hormones, glands and chemical pathways govern our feelings of attraction, lust and love. And it can be a powerful cocktail. Physiological tests have shown that an intense attraction produces a rush of dopamine - an increased concentration of which gives you a feel-good blast of euphoria and hyperactivity, as well as all those other things you associate with first love - when you don't want to eat and can't stop thinking about him. It's not innocence or naivety or the novelty of love that produces all those feelings - it's dopamine. And it doesn't matter how old you are, it can still get you. To complicate things further, it's addictive, as it creates feelings of anticipation and reward.

Hungarian researchers compared the brain scans of happily in love subjects with those who had used cocaine or amphetamines and found the same brain regions became active. But this ‘in-lust' feeling doesn't last. Scientists at the University of Pisa found that this first flush of hormones only lasts up to two years. It's then replaced with oxytocin. Known as the ‘cuddle hormone', this is an attachment chemical that bonds people - the hormonal glue that keeps couples together. But oxytocin isn't as innocent as it seems.

So, let's say, for purposes largely related to this feature, that you've slept with someone you shouldn't have. It was a mistake. You want to walk away (before he wakes up) and forget about it. But now you're feeling things you didn't feel last night. Maybe this was more than a drunken error of judgement? Stop right there. It could well be the oxytocin talking. Because it happens to be released by both men and women during sex, especially when we orgasm. But, as cruel nature would have it, testosterone, of which men obviously have far more than women, will wipe out its effects - leaving you bothered and him not so much.

Our hormones can trick us in other ways too. Research has shown that when we're at our most fertile we find men with more masculine features attractive. So show us a rugby type with a strong jaw, big smile and prominent cheekbones when we're mid-menstrual cycle and we may not be responsible for our own actions... Apart from the fact that, of course, we are responsible for our own actions. Biology and psychology aside, we choose whether or not to act on our libido. Still, at least it makes our grown-up guilty crushes feel slightly less guilty.